1. Field of the Invention
The present invention relates to a coil configuration having a tube-shaped coil brace of an electromagnetic drive, particularly a two-stage starter solenoid switch, the coil configuration having a holding winding and a pull-in winding, and the coil brace having at its one end a first delimitation and at its other end a second delimitation, between which the holding winding is situated.
2. Description of Related Art
Coil configurations of the kind described above are known. For instance, there are coil configurations of this type of two-stage starter solenoid switch of internal combustion engine starters which pose high performance and great demands on the service life. The starter solenoid switch is used to push the driving pinion of the starter into a toothed wheel of a transmission or of the internal combustion engine. In the case of single-stage starter solenoid switches, which only effect an axial shifting of the pinion, a large proportion of tooth-against-tooth positions occur, which are resolved using the large spring force of a meshing spring and using a high drive torque of the starter, whereby a high mechanical wear is created on the pinion and the toothed wheel. This is why two-stage starter solenoid switches are preferably used. They not only act to shift the pinion axially, but also act to rotate the pinion, while it is being pushed in, by a relatively small torsional current, so that the probability that teeth of the pinion mesh with the gaps of the toothed wheel of the transmission is increased.
In one known specific embodiment, a control relay switches a switching device so that the pull-in winding and the holding winding of the starter solenoid switch have current applied to them, the pull-in winding via its very low-resistance making available a torsional current to the starter motor at the same time. A relatively low current thus ensures the rotation of the pinion during meshing. During the alignment process a switch is also operated by which the starter motor is directly connected to the voltage source, so that it turns on with full torque and thereby connects the pull-in winding nearly without current. When separating the starter motor from the voltage source, since a resupply of current takes place via the pull-in winding to the holding winding, the number of turns of the holding winding has to be close to equal to the number of turns of the pull-in winding, so that the magnetic fields of the two windings mutually almost cancel out. Otherwise it is not possible to switch off the starter.
Because of a low-resistance design of the pull-in winding for providing the torsional current, and because of the specification of the equality of turns of the pull-in winding and the holding winding, the design possibilities with respect to dynamic response and a maximum admissible on-period are greatly limited. In this context, only holding windings having very high current densities are able to be used, whereby only a very brief on-period can be implemented.
Published German patent document DE 2004 032373 describes a two-stage starter solenoid switch, to which a switching device of the pull-in winding is assigned, so that a resupply of current via the pull-in winding to the holding winding is able to be interrupted. Now, since the approximate turns equality is no longer required, the designs of the windings are able to be optimized for their respective purposes. Published German patent document DE 10 2004 032373 provides a tube-shaped coil brace, in this instance, which has a first delimitation at one end and a second delimitation at the other end, a holding winding being wound up between the two delimitations, and between one of the delimitations and a pull-in winding delimitation, which is situated between the two other delimitations, a pull-in winding is wound up, so that a clear position is defined for the pull-in winding, and it does not change its position any more with the winding, or rather winding up of the holding winding.